Generally electrical cables serve the purpose of transmitting signals or power from one end to the other uninterrupted. At times, however, it is desirable to tap into the conductors at places within the length of the cable between the ends. One reason for such a break-out would be to provide a point for a branch out of additional signal or power lines from the main line. Another reason break-outs are necessary is for the attaching of active components to the cable, such as hydrophones for undersea sonar array cables.
Making the break-outs of conductors from a cable is complicated when, in addition to the electrical, optical, or mechanical components, the cable also serves as a mechanical strength member, usually loaded in tension. A common method, known in the art for strength members, is to braid a high-modulus fiber, such as Kevlar.RTM. aromatic polyamide, over the cable core prior to finishing processes, such as extrusion of the final jacket.
At the break-out point or points, one or all of the conductors may be broken out. Gaining access to the particular conductors to be broken out of the completed main cable is difficult, and generally results in partial destruction of cable components or degradation of mechanical properties at the point of breakout.
One alternative to making the breakouts from an unaltered finished cable is to make the breakouts at the time of laying up the conductors or fiber optics into a cable and leaving the ends of the broken out conductors exposed outside of the cable. At the stage of braiding the high-modulus fiber strength member around the cable, the cut ends of the conductors can be brought out through one of the openings of the braid. Then the whole construction can have a jacket extruded over it by using a tube extrusion process common in the art.
The disadvantage of using the above approach for making the breakouts are as follows. At the point of breakout, the effect is to add additional components to the cable thus effectively increasing the diameter at that point. This increase in diameter forms a "lump" in the cable which follows through all subsequent processing steps, including braiding of the strength member, and extrusion of the final jacket. If any finished cable cross-section other than round is necessary, such as an airfoil shape, then a pressure extrusion process must be used for the final jacket. One of the requirements for pressure extrusion common in the art is that the core being extruded over must have a constant cross-section, that cross-section being held to tight tolerances. Any increase in cross-section of the core, such as would occur with making breakouts, would prevent the core from passing through the extrusion tip. Another disadvantage of bringing the broken out ends out of the braid openings is the shearing action of the braid on the conductors when the cable is loaded and extended axially. As the cable is loaded in tension, the individual strands of fiber in the braid try to straighten out. The straightening out of the braided fibers and the resulting increase in cable length is normally not a problem. However, when conductors, or more importantly optical fibers, are broken out of the cable through the braid, the straightening out of the fibers of the braid produces a shearing action which tends to crush, or possibly cut through, the conductors or optical fibers.
The present invention provides for a high-strength, electromechanical optical cable with manufactured breakouts which do not increase the cable diameter. Additionally, the present invention provides for the cable to be loaded and extended axially without damage to the conductors or optical fibers housed therein at the breakout points.